1. Field of the Invention
This invention relates to a gas lens for correcting wavefront distortions that degrade a laser's far-field irradiance. More specifically, it relates to an adaptive gas lens, based on a radial jet flow of heium or other low refractive index gas such as Argon or Krypton into another gas, such as air, which is capable of providing phase corrections for a distorted annular wavefront.
2. Description of the Prior Art
Both extra-cavity and intra-cavity wavefront distortions can degrade the far-field irradiance delivered on a target by a laser. The phase of a wave-front may be controlled by changing either the path length or the velocity of propagation. The optical path length may be adjusted by moving a reflective surface such as a deformable mirror or by passing the laser beam through a transparent bar in which intense sound waves have been established which thereby acts as a diffraction grating with the deflection of the beam being controlled by the frequency of the waves. However, these optics have severe performance requirements in terms of surface accuracy and cooling.
The velocity of propagation may be changed by varying the refractive index of a medium. For instance, previous variable refraction systems have employed different types of electro-optic and magneto-optic crystals in which the index of refraction is made to vary in a controlled manner. Such refractive devices have not been generally used because of the difficulty of inducing sufficiently large changes of refractive index in devices of practical size. Furthermore, these refractive wavefront correctors previously used have a high spectral absorption, and it is difficult to obtain sufficient uniformity in the bulk material without degrading its quality.
Gas lenses for correcting wavefront distortions are not known in the prior art. Gas, or aerodynamic windows, as disclosed in U.S. Pat. Nos. 4,112,388; 4,013,977; 3,973,217; 3,949,321; 3,918,800; 3,907,409; and 3,768,038 have been utilized in place of transparent window material for passing a laser beam from an area of low pressure to an area of higher pressure. These aerodynamic windows function merely as a transparent barrier to laser medium gases. The windows do not perform the functions of the present invention, i.e., correcting wavefront distortions, nor are they designed to accomplish these functions.